Aqueous industrial functional fluids, such as metalworking fluids, are susceptible to the proliferation of microorganisms which can cause odors, deterioration, and corrosion. Antimicrobial additives (so-called preservatives) for the industrial fluids are needed to minimize the proliferation of the microorganisms. Preservatives that are effective at low doses, biodegradable, and relatively non-toxic, are desirable for environmental and economic reasons.
Pyrithione is a well-known biocide enjoying substantial commercial use as an antimicrobial agent in aqueous industrial functional fluids, such as metalworking fluids, lubricants, textile sizes, ink jet printing fluids, and the like. Sodium pyrithione and zinc pyrithione are widely employed as biodegradable fungistats in aqueous coatings, fiber lubricants, plastics, adhesives, and metalworking fluids as illustrated by the disclosures contained in U.S. Pat. No. 4,957,658.
Various basic lipopeptide antibiotics are also known, such as polymyxin B, colistin (also called polymyxin E), and octapeptin are known in the art. The primary use of these antibiotics is to treat superficial infections, as disclosed, for example, in U.S. Pat. No. 5,120,711. More specifically, the '711 patent discloses the use of antibiotics, such as polymyxin B, in combination with clotrimazole or chlorquinaldol in the preparation of synergistically active veterinary compositions useful for the treatment of mastitis and metritis. In addition, certain of these antibiotics have been disclosed as being useful in metalworking fluids, as disclosed, for example, in U.S. Pat. No. 3,359,165.
Heretofore, the combination of pyrithione and lipopeptide antibiotics has not been known for any purpose, much less in the preparation of a antimicrobial mixture exhibiting enhanced biocidal efficacy for aqueous industrial functional fluids, such as metalworking fluids. Such a antimicrobial mixture would be highly desired by the industrial fluids manufacturing community.